In the manufacture of glass fibers the glass batch ingredients are typically melted in a large melting furnace and the molten glass resulting from the melting furnace operation flows in a forehearth to a multiplicity of small glass fiber forming devices known in the art as bushings. The bushings are composed of the base plate which carries on it a plurality of nozzles or tips through which the molten glass flows in individual streams to form the glass filaments. The base plate is in turn welded to side walls forming a container having an open top into which the molten glass flows from the forehearth. The bushing is typically electrically heated to maintain the glass therein in a molten condition.
The nozzles or tips formed on the bushing bottom or base plate are relatively small in diameter and can range in number on a given bushing from 200 to 2,000 or even more. As will be readily appreciated to provide a plurality of nozzles of small diameter on the base plate forming the bottom of a bushing is a costly, time consuming process requiring great skill. Three general methods are employed in the manufacture of such nozzles or tips on base plates of bushings. These methods are described in some detail on pages 95 through 97 of the book "The Manufacturing Technology of Continuous Glass Fibers" by K. L. Loewenstein, 1973, Elsevier Scientific Publishing Company, New York.
The first method is the drop tip method which involves making an indentation on the bottom plate and with a hot flame melting wire and allowing the drops of metal to build up on the indentation. This is followed by shaping and drilling. The second method involves drilling and punching holes in the base sheet at the nozzle positions and inserting pre-manufactured solid nozzles in the holes. THe nozzles are then welded to the sheet. The last method is a cold metal drawing system which involves stamping coin like protrusions on the metal plate and cold drawing the protrusions into nozzle shape after which the nozzles are appropriately drilled. U.S. Pat. No. 3,598,952 describes the hole punching and welding system of the second method. U.S. Pat. No. 3,141,358 is exemplary of the cold metal drawing process of the last method stated above.
While all three of the processes described may be utilized to form nozzles or tips on bushing base plates they still require a considerable amount of time and effort. The cold drawing system requires several successive operations in order to draw the metal into the appropriate shapes and lengths to form a satisfactory tip or nozzle. The prepunched hole and solid insert system requires welding around each of the inserts which can be as many as 2,000 or more in a modern bushing. The drop tip method by its very nature is a tedious nozzle by nozzle system of fabrication requiring great precision, a skilled welder, and long periods of time to complete a bushing. Thus, a need still exists for the preparation of nozzles in an efficient manner that lends itself to providing on the base plate of the bushing a plurality of precisely sized nozzles required for a given bushing.